The present invention relates to a duplex electrostatic copying machine.
Duplex copying machines which form images on both sides of copy sheets have been recently devised and some have been placed on sale. However, these copying machines generally suffer from defects that the images on the opposite sides of the sheet are not in register with each other in the vertical direction of the sheet. This is caused by inaccurate sheet feed timing, especially during the formation of the second image on the back side of the sheets.
These duplex copying machines further suffer from the drawbacks that they are complicated in construction and therefore expensive to manufacture on a commercial basis. Some of these machines comprise two optical systems and two photoconductive drums or the like for forming the images on the opposite sides of the copy sheets. This duplication of basic components unnecessarily increases the cost of the copying machines.
Other forms of duplex copying machines comprise only one optical system and drum, but complicated mechanisms for turning the copy sheets over for image transfers to the front and back sides of the sheets. In addition, large space is required for the sheet turnover mechanisms, which means that the copying machines must be of excessively large overall size.